1. Field of the Invention
The present invention relates to a rock drill bit assembly primarily adapted for earth boring operations, and more particularly, to an improved rock drill bit assembly having therein a temperature-controlled, sealed environ adapted for the bearing means and lubricant disposed between the relatively rotatable parts thereof.
2. Prior Art
In the conventional earth boring operation, a rock drill bit assembly is fastened axially to the boring end of a drill string. At ground surface-level, with the drill string in the vertical position, torque is applied to the upper end of the drill string and transmitted vertically downward into the wellbore by the drill string and its rock drill bit assembly which cuts through the underlying geological formations with each successive rotation of the drill string assembly.
Generally, a rock drill bit assembly includes three basic components: a rock drill main body, at least one cone which is rotatably supported from a journal facial surface of said rock drill main body, and bearing means with their attendant lubricant positioned in the clearance space defined between the relatively rotatably opposed faces of the rock drill main body and the cone.
When a component element fails within the rock drill bit assembly during earth boring operations, it necessitates the costly operation of physically removing the entire drill string from the wellbore in order to have access to the assembly so as to replace or repair the rock drill bit assembly at ground surface-level. Accordingly, a conventional method used by the earth boring industry to economically evaluate rock drill bit assembly performance is to measure the linear footage bored prior to rock drill bit assembly failure.
Failure analysis of rock drill bit assemblies by technical experts in the earth boring industry indicates that bearing failure is the major cause of rock drill bit assembly failure. Their studies further indicate that temperature extremes during the earth boring operation destroy the lubricating properties of the lubricant or destroy the bearing means in a design where no lubricant is used, and that external contaminants present in the wellbore migrate into the clearance space between the relatively rotatably opposing faces of the rock drill main body and the cone, and that these contaminants being abrasive and corrosive in nature destroy the lubricant and bearing surfaces, and thus cause the bearing components contained therein to eventually bind, whereupon rock drill bit assembly failure occurs.
These failure analysis results bear out basic engineering theory that proper lubrication and correct temperature operating range are key factors in effecting long bearing life.
It was evident to the industry that a system using sealed lubricated bearing means would substantially prevent lubricant and bearing contamination, and that temperature-regulating means to protect the bearings and lubricant from temperature degradation within the rock drill bit assembly would greatly increase rock drill bit assembly life, and thus increase the linear footage which can be drilled per rock drill bit assembly prior to failure.
Thus, one conventional rock drill bit assembly currently in wide use and referred to as "unsealed bearing construction", is designed with a passageway in the rock drill main body which communicatively connects downhole drilling fluid in the drill string hollow core with the bearing means positioned in the clearance space defined between the rock drill main body journal facial surface and the opposing facial surface of the cone. A portion of the downhole drilling fluid is forced through this connecting passageway into the clearance space defining the bearing means environ, wherein said fluid serves to lubricate and cool the bearing elements, whereafter the spent fluid exits into the wellbore. This method of bearing cooling and lubrication causes corrosive and erosive action upon the bearing means and their respective surfaces, and tends to introduce debris contaminants into the bearing environ wherein these contaminants eventually destroy the bearing means.
A second conventional rock drill bit assembly currently in wide use and referred to as "sealed bearing construction" is designed to provide lubrication to the rock drill bit assembly bearing means by incorporating an internal reservoir cavity within the core of the rock drill main body with an ingress connecting passageway thereto to accept and equalize pressure from the wellbore environ and transmit this equalization pressure to the reservoir cavity, and an egress connecting passageway from said reservoir cavity to the bearing means environ wherein lubricant from the reservoir is transmitted to the bearing means. Lubricant stored in the reservoir is progressively squeezed therefrom so as to provide lubrication to the bearing means and their contact surfaces. In this system no direct provision is made for dissipating frictional heat generated during earth boring operations, said heat being conducted through the basically ferrous structure of the rock drill bit assembly to the bearing means and lubricant therein, where excessive heat buildup eventually destroys the lubricant and the bearing means.
Some earth boring operations are conducted in the Artic relatively close to the surface level. Conditions exist in these Artic climes where the bearing means and lubricant are thus subjected to severe cold which impairs their operation, and shortens their life expectancy unless temperature-regulation means are provided thereto.